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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials synthesis and processing 8 (2000), S. 145-153 
    ISSN: 1573-4870
    Keywords: Quartz ; alumina ; hard metals ; toxicity ; free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The release of free radicals from mechanically ground mineral dusts in aqueous suspensions has been employed to predict the possible pathogenic potential of the dusts when inhaled. Two separate free radical-generating reactions have been considered: formation of the •OH radical from hydrogen peroxide via a "Fentonlike" reaction and of a carbon centered radical, following cleavage of a carbon–hydrogen bond. The particulate examined were: variously contaminated quartz dusts, whose well-documented pathogenicity varies from one to the other source; iron- and titanium-doped alumina pigments, prepared via a mechanochemical reaction, whose pathogenic potential is unknown, and hard metal mixtures, obtained from tungsten carbide (WC) and one metal dust, namely Fe, Co, or Ni, the cobalt mixture only being a renown hazardous material. Quartz obtained by grinding coarse particles in grinding chambers composed of steel, widia, corundum, and agate, retain some characteristics of the wall chamber material, which deeply affects its capability to generate radicals and may explain the variability of quartz hazard. Insertion of ions in the mechanochemically prepared pigments imparts to the particle suspected free radical-generating properties. Among the hard metal mixtures examined, the most active is the cobalt one.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Topics in catalysis 8 (1999), S. 237-242 
    ISSN: 1572-9028
    Keywords: Pd clusters ; zeolites ; CVD ; metal particles location
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A chemical vapour deposition (CVD) procedure has been adopted for the preparation of Pd/NaY, resulting in a high dispersion of the metal phase, characterised by a bimodal distribution of particle size. The most abundant particles (80%) are about 25 Å in size, corresponding to almost twice the dimension of the zeolitic supercages. To identify their location inside or outside the zeolite matrix, the IR spectra of adsorbed CO, obtained before and after admission of NH3, have been compared. The results obtained are in sharp contrast with those for a Pd/SiO2 system, where Pd particles of comparable size are exclusively located on the external surface of the carrier. These differences support the conclusion that Pd particles in Pd/NaY are indeed located in the zeolitic cavities.
    Type of Medium: Electronic Resource
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